During his service he received three military decorations: After serving in the army, he worked for a short time as a judge in Berlin, then moved to the private sector.
Starting as an in-house lawyer, became an authorized signatory shortly thereafter, and became a partner as early as 1919[2] On 18 November 1919 he married Elise Regina Tietz (born 11 April 1896 in Munich) in Berlin.
Zwillenberg collected art, including sculptures by the animal sculptor August Gaul,[5][6] and promoted music within the Gesellschaft der Musikfreunde zu Berlin, which appointed him an honorary member for his significant services to the society on the occasion of its 25th anniversary in January 1933.
When the Nazis rose to power in 1933, the Tietz family, including Zwillenberg, was persecuted due to their Jewish heritage.
After the German occupation of the Netherlands in May 1940, the Zwillenberg family was arrested in Amsterdam on 25 October 1943, and taken to the Westerbork transit camp, where they were interned from 4 November 1943 to 15 March 1944.
Unlike the Tietz brothers, Zwillenberg did not return to Germany after the Nazi defeat, but remained in the Netherlands with his family.